Spies

ringzer0ctf

Task - intercepted transcript plus three Python 2 encryption scripts (RSA mod a prime with e=4, RSA e=5 with a deterministically padded message broadcast under many moduli, and P-521 scalar multiplication by a fixed public scalar). Solution - fourth roots mod prime via two Tonelli-Shanks passes, Hastad broadcast attack (CRT plus exact 5th root), and inverting the EC scalar modulo the group order, then concatenate the three decrypted fragments into the flag.